1. Field of the Invention
This invention relates to a traction drive tool adapter to be connected to a main shaft of a machine tool.
2. Description of the Prior Art
A prior art traction drive tool adapter consists of a rotary portion to be inserted firmly into a main shaft of a machine tool, such as a machining center, a fixed portion to be joined detachably to a fixed part of a machine tool, for example, a main shaft head thereof, and a tool mount portion to which a tool is to be attached, all of which three portions are put together via a planetary roller speed increasing mechanism.
In the rotary portion, a hollow shaft provided at the front end thereof, a grooved flange provided at the intermediate section thereof, and a taper shank provided at the rear end thereof are formed unitarily in coaxial relation.
The hollow shaft is provided at its intermediate portion with three cross-sectionally rectangular planetary roller inserting holes extending radially from the outer circumferential surface thereof into a central bore thereof so as to be spaced from one another at a central angle of 120.degree., and planetary rollers are fixed in these holes fixed rotatably to the hollow shaft via driving pins.
The rotary portion is supported rotatably on the fixed portion via ball-and-roller bearings. A housing of the fixed portion has an annular fixed raceway surface on the inner circumferential surface thereof, and the outer circumferential surfaces of the planetary rollers are engaged with this raceway surface.
The tool mount portion consists of a rotary shaft inserted rotatably in the central bore of the hollow shaft via ball-and-roller bearings, and a rear end portion, which projects rearward from a support region of the ball-and-roller bearings, of this rotary shaft constitutes a sun roller, the outer circumferential surface of which contacts the planetary rollers, a front end portion of the rotary shaft projecting from the front end of the rotary portion so that a tool can be mounted thereon.
After all, the annular fixed raceway surface, planetary rollers and sun roller form a planetary roller speed increasing mechanism, whereby the rotational speed of the rotary portion is increased to cause the tool mount portion to be rotated.
When the prior art traction drive tool adapter described above is used for a cutting and grinding operation, the depth of cut becomes excessively large due to an erroneous operation of an operator or an abnormal shape of a workpiece, so that an overload is imparted to the planetary roller speed increasing mechanism of small dimensions to cause the same mechanism to be broken.
The present invention is adapted to detect an overload on a planetary roller speed increasing mechanism in a traction drive tool adapter and prevent the same mechanism from being broken, for solving the above-mentioned problems.